Heretofore, coating of a coating solution was conducted by providing different kinds of coating solutions contained in at least one coating solution tank to a coater utilizing a common feeding tube while switching the feeding route.
In the above-mentioned method, it is necessary to wash the common feeding tube and the coater when a coating solution is switched because the feeding tube and the coater are common. In addition, when a coating solution is switched after passing water through a feeding pipe and a coater, foam is generated by the new solution in the common feeding pipe, caused by foam remaining after water is passed therethrough. When a coating solution is provided to a coater for coating without removing the foam, coating streaks and the like are caused due to the foam, which is inconvenient. Therefore, the foam is generally removed completely during the water passing step.
With regard to methods of removing foams by water-passing, a method of removing air remaining in a feeding route for a coating solution by providing deaerated water in advance to a feeding route for a coating solution after a feeding pipe and a coater that are commonly employed for a certain period of time as a detergent as described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 65824/1974 and a method of washing the common feeding pipe and coater employing deaerated hot water and an aqueous water having low surface tension are described in Japanese Patent O.P.I. Publication No. 207439/1991.
In addition, with regard to a problem of the occurrence of foam when feeding a solution, a method of preventing the occurrence of foam in a common feeding pipe by conducting operations wherein a vacuum pump is connected to a common feeding pipe by changing a valve for absorption, thereby causing a vacuum in the common feeding pipe and thereafter opening a valve of a pipe connecting tank of a coating solution which is desired to be fed when the common feeding pipe portion is closed due to closing a valve positioned at the rear portion of a common feeding pipe portion concurrently with closing of a valve of a pipe connecting a tank of a coating solution which is desired to be stopped feeding are described in Japanese Patent O.P.I. Publication No. 265639/1990.
In addition, a method of deaerating by means of heating and vacuum processing is described in Japanese Patent Publication No. 43722/1987.
Owing to the conventional methods described above, washing inside a common feeding pipe and prevention of remaining foam became possible. However, problems lie in a coater unit, too. Namely, heretofore, deaerated water for removing foam was provided inside of a coater. In such a case, when deaerated water is replaced with a coating solution in the succeeding step, replacement efficiency is poor so that uneven replacement occurs. In addition, when still foam occurs after water cleaning, foam is allowed to remain in a coater. Accordingly, as a measure to prevent foam, formation a thin film was inserted into the slits of a coater and drawn to the depth direction and the width direction so that uniform replacement inside a coater is obtained and removal of any remaining foam are conducted. The above-mentioned operation is performed manually. This thin film is applied to all slits (having 7 to 16 layers). This procedure causes a noticeable loss in time, deteriorating production efficiency remarkably. In addition, according to the conventional methods, constant loss in solution is so noticeable that it is disadvantageous in terms of reduction in production cost.
As described above, according to the conventional methods, loss occurred when time and solution in changing to a new coating solution after passing water through a line (a common feeding pipe) and a coater. If the above-mentioned losses in replacement can be eliminated, time necessary for switching a coating solution and loss in solutions can be saved remarkably, improving production efficiency noticeably.